Service providers are evolving the existing time division multiplexing (“TDM”) based circuited networks to packet-based networks and eventually to end-to-end internet protocol telephony applications using session initiation protocol (“SIP”) as the signaling protocol. A typical session initiation protocol network architecture may consist of one or more session initiation protocol back-to-back user agents (“B2BUA”) and session initiation protocol user agents (“UA”). The session initiation protocol user agents employ specific coder-decoder (“codec”) formats to communicate with other network entities. The session initiation protocol user agents employ codec negotiation to set up communication with other session initiation protocol user agents.
Several network configurations exist that require codec negotiation. Exemplary configurations include a wireless telephone to public switched telephone network (“PSTN”) call, a wireless telephone to wireless telephone call when the wireless telephones employ a compatible codec format, and a wireless telephone to wireless telephone call when the wireless telephones employ different codec formats.
As one shortcoming, a session initiation protocol user agent employing one codec format cannot communicate with a session initiation protocol user agent employing a different codec format. Different session initiation protocol user agents may employ different codec formats. For example, wireless session initiation protocol user agents may support codec formats such as adaptive multi-rate (“AMR”), global system for mobile communications full rate (“GSM FR”), global system for mobile communications half rate (“GSM HR”), enhanced variable rate codec (“EVRC”), Qualcomm code excited linear prediction (“QCELP” or “13k”), and/or selectable mode vocoder (“SMV”). Landline session initiation protocol user agents may support the codec formats of the wireless session initiation protocol user agents as well as other codec formats typically used in landline networks, such as G.711, and/or adaptive differential pulse code modulation (“ADPCM”). The session initiation protocol employs session description protocol (“SDP”) offer/answer procedures to perform media codec negotiation between session initiation protocol user agents in a session initiation protocol network. If the session initiation protocol user agents do not support one or more common codec formats, then session initiation protocol cannot successfully establish a communication session between the session initiation protocol user agents.
Thus, a need exists for enhanced codec negotiation in a variety of network architecture configurations.